.\"	$OpenBSD$
.\"
.\" Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
.\"
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate$
.Dt RSYNCD 5
.Os
.Sh NAME
.Nm rsyncd
.Nd rsyncd wire protocol
.Sh DESCRIPTION
The
.Nm
protocol described in this relates to the BSD-licensed
.Xr openrsync 1 ,
a re-implementation of the GPL-licensed reference utility
.Xr rsync 1 .
It is compatible with version 27 of the reference.
.Pp
The
.Nm
protocol is an envelope protocol for
.Xr rsync 5
between a client and an rsync://-capable server.
It provides a means to exchange capabilities information prior to file
transfer.
.Pp
In this document,
.Qq client
refers to the
.Xr openrsync 1
utility making the request.
It follows that
.Qq server
refers to the daemon servicing the request.
.Pp
A connection between a client and server consists of host, a module, and
zero or more paths.
.Pp
.Dl openrsync rsync://host/module/path1 rsync://host/path2... dest
.Pp
At this time, operating in sender mode (with the rsync:// host receiving
information) is not described in this document.
.Ss Data types
These are the same as in
.Xr rsync 5 .
A newline is always a standalone \en.
.Ss Client process
After initialising a connection, the client and server exchange the
following information, in order.
This portion of the process is
.Em not
multiplexed.
.Pp
.Bl -enum -compact
.It
client sends requested module followed by newline
.It
server responds with preamble followed by standalone newline
.El
.Pp
The requested module must have non-zero length.
The preamble consists in a sequence of lines.
Each line either contains free-form text sent by the server as a
.Qq motd
.Pq message of the day
or a command:
.Pp
.Dl @RSYNCD: command\en
.Pp
The only supported command is the server protocol specification:
.Pp
.Dl @RSYNCD: xx[.yy]\en
.Pp
The optional component is the submodule, which may be discarded.
The version may only be specified once.
Both the motd and commands end in the special termination command:
.Pp
.Dl @RSYNCD: OK\en
.Pp
Following that, the client must send the command-line arguments that
would otherwise be used to start a
.Xr openrsync 1
server.
Each argument must be specified on its own line, e.g.,
.Pp
.Dl --server\en--sender\en-r\en-t\en.\enpath1\enpath2
.Pp
This must be followed by a standalone newline.
.Pp
If the server does not understand or accept any of the command-line
arguments, it will exit at this point.
.Pp
Following this, the client must read the integer-length session checksum
seed.
Multiplexing is subsequently enabled.
.Pp
The sequence that follows is stipulated in
.Xr rsync 5
following the handshake.
.\" The following requests should be uncommented and used where appropriate.
.\" .Sh CONTEXT
.\" For section 9 functions only.
.\" .Sh RETURN VALUES
.\" For sections 2, 3, and 9 function return values only.
.\" .Sh ENVIRONMENT
.\" For sections 1, 6, 7, and 8 only.
.\" .Sh FILES
.\" .Sh EXIT STATUS
.\" For sections 1, 6, and 8 only.
.\" .Sh EXAMPLES
.\" .Sh DIAGNOSTICS
.\" For sections 1, 4, 6, 7, 8, and 9 printf/stderr messages only.
.\" .Sh ERRORS
.\" For sections 2, 3, 4, and 9 errno settings only.
.Sh SEE ALSO
.Xr openrsync 1 ,
.Xr rsync 5
.\" .Sh STANDARDS
.\" .Sh HISTORY
.\" .Sh AUTHORS
.\" .Sh CAVEATS
.\" .Sh BUGS
